The present invention relates to the field of optical information storage and retrieval systems and, more particularly, to an optical disc cartridge with a flexible storage medium stabilized during rotation by a Bernoulli surface.
The present emphasis in the development of information storage systems is to increase the amount of information stored in so-called "desk-top" sized computer memory system. Desk-top sized memory systems which incorporate magnetically recorded hard disc storage media, such as that used in Winchester-type disc drive memory systems, currently have the capacity to store upwards of 200 megabytes of magnetically recorded information. The problem with such memory systems is that, by necessity, the hard disc storage medium is permanently mounted into the computer. Since the storage medium is not easily removable, the user is restricted to utilize only those portions of the hard disc that remain available for information storage at the time of use. Accordingly, information systems employing magnetically-recorded hard disc storage media are not perceived as potential solutions to the problem of increasing information storage capacity.
Unlike hard disc systems, the so-called "floppy disc" memory storage systems use flexible magnetic discs, each having a diameter of either 5.25 inches or 3.50 inches, as the storage media. These floppy discs can be easily removed and/or interchanged. However, the magnetically recorded information storage capacity of a single floppy disc has not yet reached a level equal to that of the hard disc. A single floppy disc can only store approximately 1 to 2 megabytes of magnetically recorded information. Nonetheless, floppy discs are frequently used as a magnetic storage medium despite their storage limitations primarily because of their portability and low cost.
Several magnetic disc storage products have been recently introduced which attempt to bridge this gap between the capacities of magnetic hard discs and magnetic flexible discs. The primary goal of these products has been to provide a removable disc package which has more capacity than a single floppy disc. Additionally, another goal of these products has been to provide a high performance disc drive which increases the data transfer rate and reduces the disc access time as compared to the corresponding characteristics of a conventional floppy drive. Two of the techniques which have been used to design these intermediate products are: 1) to design the hard disc packaging which can be removed from the disc drive; and 2) the introduction of features into floppy discs which allow the disks to operate as a rigid disc.
It is well known that the space between a magnetic disc and its transducer is critical for proper data storage and retrieval. Maintaining this critical gap is a primary engineering problem which must be addressed when designing a product which uses flexible media and performs similar to a rigid disc drive. A technique which has been used to flatten and stabilize the floppy disc during the read/write operation, in order to facilitate control of the gap, is to rotate the disc at high speeds in close proximity to a flat surface sometimes called a Bernoulli plate. In such a configuration, an air bearing is formed between the Bernoulli plate and the floppy disc so that a fixed gap between the recording surface of the floppy disc and the Bernoulli plate is created and maintained. When the gap between the disc and the plate has been stabilized sufficiently, the gap between the disc and the transducer can similarly be reduced and performance of the disc drive is enhanced.
In order for the Bernoulli plate to be effective, however, the surface of the plate must be flat and rigid, especially in the region of the plate where the transducer is positioned. For this reason, most applications of this technology have fixed the Bernoulli plate completely or partially within the disc drive. See U.S. Pat. No. 3,947,886 issued to Heidecker and U.S. Pat. No. 4,074,330 issued to Norton et al. In an alternative configuration, however, the Bernoulli surface need not be contained in the disc drive to provide sufficient stabilization for the media; it may be enclosed within the cartridge, itself. Rotating a magnetic disc in proximity to a surface inside a disc cartridge is not new in the art. For example, see U.S. Pat. No. 3,772,665 issued to Hertrich. U.S. Pat. No. 4,734,989, issued to Bauck, et al, discloses the use of a Bernoulli surface placed within a disc cartridge proximate a flexible magnetic disc in order to stabilize the magnetic disc during rotation. However, Bauck, et al, includes a slot-shaped opening in the stabilizing Bernoulli surface in order to permit information transfer from the magnetic disc to the transducer. Thus, in such a design, the effects of Bernoulli stabilization on the magnetic disc are weakest at the point where precise spacing is most critical--the physical location on the magnetic disc where information storage and/or retrieval is occurring.
An additional technology which attempts to bridge the gap between the utility and removability of magnetic floppy discs and the performance of magnetic hard discs has been the advent of optical information storage systems. Optical storage systems have become increasingly popular in recent years. In general, an optical disc storage system operates by rotating an optical disc around a central axis. A light beam is projected onto the surface of the disc by an optical head assembly which typically includes a light source, a collimating lens, a reflecting mirror and a projecting lens. During read operations, or in a so-called worm (write once, read many times) drive, light is projected by the optical head assembly onto a specific location on the optical disc. Modulated reflected light detected by a photodetector and supplied to a data processor for producing information signals.
In an optical system during write operations, the light intensity is modulated by the optical head. The optical disc contains an active layer which is sensitive to the intensity of incident light. Consequently, the light intensity produced by the optical head is increased so as to cause a change in this active layer at the point o the disc at which the light is focused. This change can be sensed during writing itself or can be detected at a later time during a read operation as described above.
Information storage systems which can be accessed through optical devices such as the one described above have recently received serious attention due to their potential capacity to store substantial amounts of data, i.e. on the order of 400 to 800 megabytes of information, utilizing the same physically sized devices that are currently in use. This capacity represents an increase of a factor of 4 over that currently available in magnetically recorded hard discs and a factor of 400 over floppy disc storage systems.
Most all optical discs designed for minicomputers an microcomputers, which are presently in commercial operation, are comprised of a rigid plastic or glass substrate with a thin, optically active layer deposited thereon for the storage of information. Such a design has proven desirable for several reasons. First, in order to maintain a relatively constant distance between the active layer and the optical head to ensure proper transfer of information, a rigid optical disc, once properly positioned within the disc drive, will spin in a predetermined and consistent fashion. Unfortunately, the relatively high cost of manufacturing rigid optical discs has inhibited widespread commercial acceptance of optical information storage systems. However, the storage media used in such optical systems need not be rigid. The media can be of a form similar to that of a floppy disc, that is, a media which is both easily removable and more cost effective.